Various types of paper sheet stacking mechanisms have been used which include a stacking wheel for stacking paper sheets, such as banknotes, checks, and securities in an aligned state (refer to JP2011-180732A, for example). The stacking wheel of the conventional paper sheet stacking mechanism includes vanes disposed on the outer periphery thereof at regular intervals. While the stacking wheel is rotating, each paper sheet enters the gap between two adjacent vanes of the stacking wheel and is transported by the rotation of the stacking wheel. After the front end edge of each paper sheet transported by the rotating stacking wheel comes into contact with a guide member, the paper sheet is released from the gap between the vanes and is stacked in the stacking unit in an aligned state.